Anaglyph stereoscopy is a well-known process in which left and right images are color encoded by respective complementary color filters (e.g. cyan and red) for viewing through corresponding glasses to separate the images as required for a three-dimensional effect.
U.S. Pat. No. 3,712,199 of Songer, Jr. discloses an anaglyph stereoscopic imaging system in which a "compatible" two-dimensional picture is taken through a single lens. The photographic print is "compatible" in the sense that when it is viewed without filtered glasses, the image appears to be a normal two-dimensional image; however, when viewed through appropriately filtered glasses, a three-dimensional image is seen.
Essentially, in the Songer system, three-dimensional information is derived from defocus components of the objects to be photographed. Thus, if an object is sharply focused on to image plane of the camera, an object closer to the camera would normally be focused beyond the image plane. An object further from the camera would be sharply focused in front of the image plane. It can be shown that closer objects traverse the image plane with a defocus blur in the same sense as through the lens whereas further objects traverse the image plane with a defocus blur in the opposite sense. If complementary color filters cover horizontally opposite sides of the lens, a focused image will appear in normal full color, while defocused objects will have left and right borders encoded as described above. For example, if cyan and red filters are used, objects closer to the camera may have a red fringe on the right side and a cyan fringe on the left side. Objects further from the camera would have a red fringe on the left side and a cyan fringe on the right side. When viewed without the aid of glasses, these fringes do not materially affect the normal two-dimensional aspect of the picture; however, when viewed through corresponding filters, the left and right encoded images are combined to create a three-dimensional perception of the scene.
For a more complete understanding of anaglyph stereoscopy, reference is made to the aforesaid Songer patent which is hereby incorporated by reference into this specification.
In the Songer system it is necessary to introduce the color filtration at or near the aperture stop plane (which includes the iris or diaphragm opening) of the taking lens assembly of the camera to achieve the desired results. Therefore, each lens assembly to be used must be modified by the addition of appropriate complementary color filters. This is undesirable from a practical point of view when dealing with a family of lenses and/or complex and costly lenses, for example, of the zoom type.
Additionally, the Songer system causes a degradation of dstereoscopic information as the iris (diaphragm) opening is diminished. The light which traverses the optical system is determined by the available light, the opening of the iris, and the shutter speed. Conventionally, camera irises are round and the aperture is varied in two dimensions (i.e. both vertically and horizontally).
In the Songer system, the horizontal dimension of the iris determines the amount of useful fore and aft defocus and, hence, the stereoscopic separation of the images. Accordingly, with a standard round iris or diaphragm, as the size of the aperture is decreased, the three-dimensional effect is decreased.